Samstag, 23. August 2014

Going oudoors with the RTLSDR

I decided to write this post in English, so it could reach more readers and help them by using the RTLSDR in a portable way. I'm not a native English, but I'll try my very best to make it readable without causing to much headache ;-)

Using the RTLSDR on the Schneeberg, 1051m above sealevel

Why should you go outside with your RTLSDR?

There are some really good reasons, why using the dongle in the field is a great pleasure!
Many of us don't have the best situation for receiving, living in little flats not really high over the ground and without the capabilities of using real antennas like the big yagis. By climbing on little mountains, you can improve this situation a lot. Just test it and compare the spectrum of your SDR with the one at home and you'll see, what I mean. Especially in the VHF and UHF band, the effect is great! On these frequencies, the electromagnetic waves behave like light, if you can (virtually) see a transmitter, then you should be able to receive it. That's why getting up from the ground is so important and people are building huge towers in their garden.
The other point is, you get away from many unwanted emissions, caused by modern electronics. That's a really big problem the shortwave guys have, but on the higher bands it's a problem, too.
By the way, going outdoors is always a good idea, especially when you climb on hills!

What do you need?

You don't that much for using the RTLSDR (or any other SDR you use) portable. I would bet, you already have the most of the useful things, but maybe I can give you some additional hints for making it more fun.
Of course, you need a RTLSDR dongle and a notebook. Using the dongles with an Android tablet is possible, but it feels to limited for me. Maybe the new Windows tablets are the way to go, but since I don't own one of these, I couldn't write anything about it. @LondonShortwave on twitter shows photos from time to time showing his portable gear, so be sure to follow him to get instant updates!

The notebook

Of course, a light and small notebook is the way to go, because you have to carry it the whole trip. But even if it's not one of the fancy new ultrabooks, you can use it although. I'm using a Lenovo T420 and it's not one of the biggest ones, but you can't compare it a nice ultrabook or one of the subnotebooks on the market.
What's really important, you need a very bright screen, especially when it's a glare one. I have to use my display on the brightest setting most of the day when I'm outside. And of course, even in this battery draining state, it should work long enough for our purposes. Remember, using SDR software like SDR# and SDR-Radio is quite challenging for the CPU!
Of course, there are additional batteries and even solar panels that can extend the runtime of your notebook a lot, but it depends on your intentions, if they are really necessary. In an hour of receiving with a SDR, you can record enough stuff to work with it for many days. That's really a great feature to mention here, using the record function of your SDR software is so much fun. You can just record all the signals and analyze them at home, where it's warm, dry and you have connected your notebook to the powerline. But remember, it's quite a lot of data, recording the whole spectrum of a RTLSDR, or even an HackRF!
Today, SSD's seem to be usual in notebooks and they are the way to go in a portable receiving machine, since they are fast and don't care about any mechanical influences wile receiving signals in the field. I'm using a SSD as the main drive in my Lenovo and a HDD in the Ultrabay instead of a CD-ROM, so I have the speed of the SSD and the space of a HDD in one portable pack.

The dongle

It makes no difference from using your dongle inside your house or outdoors, so there's nothing special to mention here.

The antenna

It's a known rule, that a good antenna is the best amplifier you can use. There is nothing special when you operate your dongle portable. I'm using a Diamond RH77 that's build for using it on a handheld transceiver. When using one of those antennas on a dongle, you should add some pieces of wire to the ground of the antenna plug, so it looks like a simple groundplane, since they work worse, if there isn't a HT with some metal on their base.
There are other antennas as well, but for me it seems, most manufacturers concentrate on building portable antennas for the lower bands. In the US, there are directional antennas build by Arrow Antenna or Elk, but these don't seem to be available in Germany. Wimo just added a SOTA antenna, maybe I'll give it a try.
Another nice manufacturer is Lambdahalbe, they build antennas made of wire and are really portable. Just throw a rope on a tree and hang the antenna as high as you like it to be. Because of there construction, they work best if they are away from any conducting material, so the tree former mentioned is perfect.

The accessoires

You'll need an USB extension, I always carry two different in my bag. One is about one meter, the other one is three meters long. If you buy one, be sure to check it at home, as some won't work properly, especially the ones longer than three meters. I've purchased my long USB cable from Amazon basics and even using both cable together works flawlessly.
A padded sleeve saves your notebook from scratches and you can use it as a spacer so you don't have to lay your notebook on any muddy surfaces.
Depending on the antenna your using, you should carry some material to mount it properly. Using the Lambdahalbe antenna, I'm carrying a few meters of a 2mm rope with me. The people at Nite Ize have many great tools, that are really handy using the RTLSDR portable. Using the Figure 9 Carabiner, you can easily secure the rope and connect it with the antenna.
If you're using a HT antenna, you could use the Gear Ties from Nite Ize, to mount it properly.
Of course, you need a proper bag to carry all your gear, but since the market is so big and I assume, most of you already own one, I'll jump over this topic.

As you can see, there isn't really any special equipment needed for using your RTLSDR outdoors. Of course, you can extend this to the finest gear available, using rugged notebooks like ToughBooks, protect them using carrying gear from Peli and so on. But you don't need this to have some fun in the field!